Vulnerable Missouri Sen. Claire McCaskill's (D) campaign is on the air with two radio ads pushing back against spots attacking her.

The first McCaskill spot, which responds to and matches the buy size and targeting of a state Republican Party ad, has been on the air for about a week.

"This is Missouri," a folksy male announcer intones in the ad. "We know false prophets when we hear 'em. No one believes what they're saying about Claire McCaskill."

The second McCaskill spot, which responds to and matches the buy size and targeting of a Crossroads GPS ad ($65,000 statewide), directly responds to issues about birth control alluded to in the GPS ad. That spot started airing Thursday night.

"Claire McCaskill is fighting to prevent abortion," a female announcer says. "She wants all women to have access to affordable birth control. No government can tell a woman if she can use birth control."

The dueling spots are part of the larger political fallout from President Barack Obama's decision to walk back a mandate on birth control under the Patient Protection and Affordable Care Act.